Disable an optimisation that turned out to be a pessimisation (replacing...

Disable an optimisation that turned out to be a pessimisation (replacing literal lists with tuples).

Cython/Compiler/Optimize.py

@@ -2835,8 +2835,11 @@ class OptimizeBuiltinCalls(Visitor.NodeRefCleanupMixin,
         if value.mult_factor is not None or len(items) > 8:
             # Appending wins for short sequences but slows down when multiple resize operations are needed.
             # This seems to be a good enough limit that avoids repeated resizing.
-            if isinstance(value, ExprNodes.ListNode):
-                # At least avoid the list building and use a faster tuple instead.
+            if False and isinstance(value, ExprNodes.ListNode):
+                # One would expect that tuples are more efficient here, but benchmarking with
+                # Py3.5 and Py3.7 suggests that they are not. Probably worth revisiting at some point.
+                # Might be related to the usage of PySequence_FAST() in CPython's list.extend(),
+                # which is probably tuned more towards lists than tuples (and rightly so).
                 tuple_node = args[1].as_tuple().analyse_types(self.current_env(), skip_children=True)
                 Visitor.recursively_replace_node(node, args[1], tuple_node)
             return node